The present invention relates to batch mixers which mix polymeric materials such as plastics and rubber and, in particular, to a hopper door-locking mechanism for such mixers.
The mixing of raw materials, such as plastics and rubber, is often performed in batch mixers, such as a so-called "Banbury" mixer described, for example, in U.S. Pat. No. 4,818,113. Such a mixer 10, depicted herein in FIG. 1, includes a mixing body 12 and a feed hopper 14 for supplying the raw material to the mixing body. The mixing is performed by rotors 16 which are rotated at identical or different speeds within a mixing chamber 18 of the mixing body 12. A ram 20 is provided which can be lowered downwardly onto the mix within the mixing chamber to aid in the mixing operation. Heat is supplied to the mixing chamber by circulating hot oil or steam through passages 21 formed in the mixing body 12.
A hopper body of the feed hopper 14 has a door 22 which can be opened to enable raw material to be fed to into the hopper. A fluid-actuated cylinder 24 is utilized to open and close that door. The door 22 swings about a horizontal axle 26 disposed along a lower edge of the door and travels between a pair of guide projections 28 of the hopper body. A drop door 30 closes the bottom of the mixing chamber 18 and is latched by a piston rod 32.
During operation, raw materials and/or scrap materials are loaded into the mixing chamber from the hopper. The hopper door is closed, the ram is lowered, and the rotors are rotated until the proper temperature and mixing time have been achieved. Additional raw materials or scrap can be added as necessary. A problem can occur in the event that water enters the mixing chamber, e.g., if wet scrap is used. As the mix heats up, the water can suddenly turn become converted to steam. The resulting pressure increase may be great enough to force the ram 20 upwardly and overcome the pressure of cylinder 24 to push the hopper door 22 open, allowing molten material to blow out of the mixer in an uncontrolled manner. Serious harm to adjacent personnel and equipment can occur when such a blow-out occurs.
It would be desirable, therefore, to be able to eliminate dangerous blow-outs of that type.